Technical Field
This disclosure relates generally to valves for shutting off flow in a pressurized pipe or conduit. More specifically, this disclosure relates to gate valves that are installable on a pressurized pipe without shutting off flow through the pipe during installation. Still more specifically, this disclosure relates to improvements in the designs of such gate valves, including a mechanism for equalizing the pressure above the gate valve and within the gate valve housing to that of the pressurized pipe during operation of the gate valve assembly.
Description of the Related Art
Pressurized conduits or pipes convey fluids, both liquid and gas, in municipalities, industrial plants and commercial installations. When originally installed, a network of pipes may include isolation valves used to isolate certain sections of the pipe for repairs, relocation, installation of new components into the pipe, etc. However, a shutdown closing one or more isolation valves of part of a municipal water system or other fluid distribution system may deprive a large area of water service resulting in inconvenience to residents, schools, hospitals, commercial and/or industrial facilities.
The length of pipe of a water system that needs to be isolated can be shortened and fewer people inconvenienced by adding additional valves, in conjunction with the preexisting block valves. Currently, installation of additional valves on a pressurized pipe does not require service interruption and results in minimal fluid or pressure loss. The additional valves connect to the pipe as an assembly with a nozzle and/or installation housing. After removal of the installation housing, the nozzle accommodates the valve in an open position. Upon closure of the added valve and completion of the work on the depressurized damaged section of the pipe, an operator opens the additional valve retracting it back into the nozzle thereby restoring flow through the repaired section of pipe. The additional valves are known as insertion valves, add-on valves, insertable gate valves, etc. Exemplary gate valves are disclosed in commonly assigned U.S. Pat. Nos. 6,810,903, 8,627,843 and 9,644,779. An advantage provided by the systems of the '903, '843 and '779 patents is that only a portion of the cross-section of the pipe is removed to install the valve. As a result, the integrity of the pipe section is maintained. In contrast, installation of many standard valves requires an entire section of pipe to be removed and replaced with a new section that includes the added valve.
Returning to systems like those shown in the '903, '843 and '779 patents, the nozzle is clamped perpendicularly and pressure-tight to the outside of the pipe by a saddle assembly as shown in FIGS. 1 and 15 of the '903 patent. An installation housing is typically mounted on top of the nozzle with a temporary valve disposed therebetween as shown in FIGS. 1 of the '903 patent and FIGS. 2-7 of the '843 and '779 patents. A process known as pressure tapping, hot tapping or under-pressure tapping forms an opening in the pipe thereby establishing communication between the nozzle and the pipe. This process is well known in prior art, and utilizes the temporary valve to allow a cutting device to pass from the installation housing and through the temporary valve and nozzle before cutting a hole in the pipe without significant loss of fluid pressure, which is contained by the installation housing. After cutting the opening in the pipe, a feed screw moves the additional gate valve from the installation housing, through the temporary valve and into the nozzle, where it may be sealably set in place. See FIGS. 3, 19 and 21-22 of the '903 patent, FIG. 10 of the '843 patent and FIG. 8 of the '779 patent. After removal of the installation housing and the temporary gate, the nozzle may be equipped with a cover plate having an opening for the gate stem. An accommodating operating nut is fixedly attached to the gate stem so the nozzle, gate valve and saddle assembly may form a permanent installation on the pressurized pipe. An operator may open and close the gate valve by turning the operating nut with a handle or wrench.
As shown in FIGS. 10-14 of the '903 patent, FIG. 12 of the '843 patent and FIG. 9 of the '779 patent, the gate valve forms a seal directly on the inside surface of the host pipe. The problem with sealing on the inside face of any pipe is that the condition and internal diameter of the pipe can vary so the sealing element must be able to expand to cover a range of internal pipe conditions and diameters. As a result, there is a need for sealing elements that can expand radially to seal a variety of pipe internal diameters while enduring the enormous forces that come from high flow and high-pressure lines.
The sealing elements described in the '843 and '779 patents “generally U-shaped” “paddle(s).” The paddles are supported by structures known as a “cartridge” or a “bullet.” As shown by the wiper seal 124 of FIG. 11 of the '843 patent and by the wiper seal 118 of FIG. 9 of the '779 patent, a sealed pressure zone is created above the wiper seals 124, 118 and within the nozzles 50 when the wiper seals 124, 118 begin interacting with the interior nozzle surface upon closing the gate valves. This sealed, pressurized zone of incompressible fluid (i.e., water) will prohibit upward vertical movement of the gate valve to open the gate valve if a path is not made available for fluid above the gate valve to escape. As a result, there is a need for a pressure relief, which correlates to the vertical movement of the gate valve assembly.
Accordingly, needs exist for improved gate valve assemblies for installation in pressurized pipes and conduits that address these problems.